Anisotropic Cell Expansion Is Affected through the Bidirectional Mobility of Cellulose Synthase Complexes and Phosphorylation at Two Critical Residues on CESA3

Abstract

Here we report that phosphorylation status of S211 and T212 of the CESA3 component of Arabidopsis (Arabidopsis thaliana) cellulose synthase impacts the regulation of anisotropic cell expansion as well as cellulose synthesis and deposition and microtubule-dependent bidirectional mobility of CESA complexes. Mutation of S211 to Ala caused a significant decrease in the length of etiolated hypocotyls and primary roots, while root hairs were not significantly affected. By contrast, the S211E mutation stunted the growth of root hairs, but primary roots were not significantly affected. Similarly, T212E caused a decrease in the length of root hairs but not root length. However, T212E stunted the growth of etiolated hypocotyls. Live-cell imaging of fluorescently labeled CESA showed that the rate of movement of CESA particles was directionally asymmetric in etiolated hypocotyls of S211A and T212E mutants, while similar bidirectional velocities were observed with the wild-type control and S211E and T212A mutant lines. Analysis of cell wall composition and the innermost layer of cell wall suggests a role for phosphorylation of CESA3 S211 and T212 in cellulose aggregation into fibrillar bundles. These results suggest that microtubule-guided bidirectional mobility of CESA complexes is fine-tuned by phosphorylation of CESA3 S211 and T212, which may, in turn, modulate cellulose synthesis and organization, resulting in or contributing to the observed defects of anisotropic cell expansion.

Increase in Cell Wall Thickening and Biomass Production by Overexpression of PmCesA2 in Poplar

“…Cellulose biosynthesis and secondary wall thickness of Arabidopsis are affected by mutations in each of the secondary CesAs (CESA4/IRX5, CESA7/IRX3, and CESA8/IRX1), leading to collapsed xylem phenotype (Turner and Somerville, 1997;Taylor et al, 1999;Taylor et al, 2000;Taylor et al, 2003). Mutations in each of the primary CesAs can lead to reduced organ growth, which has been interpreted as the consequence of growth anisotropy being lost (Pagant et al, 2002;Fujita et al, 2013;Chen et al, 2016). CesA5 and CesA2 are responsible for secondary wall cellulose biosynthesis in Arabidopsis seed coat epidermis (Mendu et al, 2011).…”

Secondary cell wall biosynthesis

“…Mass spectrometry analysis of Arabidopsis CESA7 revealed two phosphorylation sites in the CSR of its catalytic domain (Taylor, ). Although the significance of phosphorylation of secondary wall CESAs on their functions has not been examined, phosphorylation of a primary wall CESA, CESA3, has been demonstrated to be involved in fine‐tuning the microtubule‐guided bidirectional mobility of CESA complexes (Chen et al ., ). Secondary wall CESAs have also been shown to be S‐acylated, that is, modified by addition of an acyl group, such as palmitate or stearate, to a cysteine residue (Kumar et al ., ).…”

BRASSINOSTEROID INSENSITIVE2 negatively regulates cellulose synthesis in Arabidopsis by phosphorylating cellulose synthase 1

“…S2), suggesting that BIN2 might influence cellulose production, potentially through its protein kinase activity. Many CSC subunits can become phosphorylated at multiple positions (29)(30)(31)(32), and some of these phosphorylation events have been demonstrated to regulate the CSC functionally (14,33,34). However, the corresponding protein kinases have remained unidentified.…”